| Abstract: | The equilibria involving gaseous species above the condensed Cu-Sn system have been experimentally investigated at elevated temperatures by the high temperature mass spectrometric technique. The molecules CU₂, CuSn, Sn₂, Cu₂Sn, CuSn₂, and Sn₃ were found to exist in the vapor phase above the liquid Cu-Sn alloy which is predominantly atomic in composition. Third-law enthalpy changes have been determined from the experimental data for the following gaseous reactions: CU₂ = 2Cu, Sn₂ = 2Sn, Sn₃ = 3Sn, CuSn = Cu + Sn, CU₂Sn = 2Cu + Sn, Cu₂Sn = Cu₂ + Sn, Cu₂Sn = Sn + 2CuSn, CuSn₂ = Cu + 2Sn, CuSn₂ = Cu₂+ Sn , CuSn₂ + Cu = 2CuSn. The values of the reaction enthalpies have been combined to give the bond dissociation energies, D_o^o, of the diatomic molecules, and the atomization energies, ∆H_(ATM,o), of the various triatomic molecules assuming different molecular structures for the latter. The previously known molecules Cu₂, Sn₂, Sn₃, and CuSn, have been evaluated, yielding atomization energies of 48.1 ± 2.0, 44.2 ± 1.0, 103.2 ± 0.4, and 39.8 ± 2.0 kcal mole⁻¹ respectively. These values agree within the quoted error limits with the reported literature values. The atomization energies, ∆H_(ATM,o), (in kcal mole⁻¹) are presented for the previously unreported molecules: Cu₂Sn (linear symmetric, 107.9 ± 5.3; bent symmetric, 103.6 ± 5.2; linear asymmetric, 106.7 ± 5.3; bent asymmetric, 102.7± 5.2) and CuSn₂ (linear symmetric, 95.8 ± 2.6; bent symmetric, 95.3 ± 2.6; linear asymmetric, 97.4 ± 2.6; bent asymmetric, 87.9 ± 2.6). The values of the heats of atomization for CU₂Sn and CuSn₂ were averaged to be 106.0 ± 2.5 and 93.8 ± 4.2 kcal mole⁻¹, respectively. The heats of formation, ∆〖H°〗_(f,o), of CU₂Sn and CuSn₂ were 127.0 ± 2.5 and 130.7 ± 4.2 kcal mole⁻¹, respectively. |
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